108 



SIR H. DAW S AGRICULTURAL CHEMISTRY. 



lobes, and radicle is the small curved cone 

 at their base. 



In wheat, and in many of the grasses, 

 the organ of nourishment is a single part, 

 and these plants are called monocotyle- 

 dunous. In other cases it consists of 

 more than two parts, when the plants are 

 called phycotyledonous. In the greater 

 number of instances, it is, however, simply 

 divided into two, and is dicotyledonous. 



The matter of the seed, when examined 

 in its common state, appears dead and 

 inert; it exhibits neither the forms nor 

 the functions of life. But let it be acted 

 upon by moisture, heat and air, and its or- 

 ganized powers are soon distinctly deve- 

 loped. The cotyledons expand, the mem- 

 branes burst, the radicle acquires new mat- 

 ter, descends into the soil, and the plume 

 rises towards the free air. By degrees, the 

 organs of nourishment of dicotj.'ledonous 

 plants become vascular, and are converted 

 into seed leaves, and the perfect plant ap- 

 pears above the soil. Nature has pro- 

 vided the elements of germination on 

 every part of the surface; water and pure 

 air and heat are universally active, and 

 the means for the preservation and multi- 

 plication of life, are at once simple and 

 grand. 



To enter into more minute details on 

 the vegetable physiology would be in- 

 compatible with the objects of these lec- 

 tures. I have attempted only to give 

 such general ideas on the subject, as may 

 enable the philosophical agricultui'ist to 

 understand the functions of plants; those 

 who wish to study the anatomy of vege- 

 tables, as a distinct science, will find 

 abundant materials in the works of the 

 authors I have quoted, page 9, and like- 

 wise in the writings of Linnseus, Desfon- 

 taines, Decandolle, de Saussure, Bonnet, 

 and Smith. 



The history of the peculiarities of 

 structure in the different vegetable classes, 

 rather belong to botanical than agricul- 

 tural knowledge. As I mentioned in the 

 commencement of this lecture, their or- 

 gans are possessed of the most distinct 

 analogies, and are governed by the same 

 laws. In the grasses and palms, the cor- 

 tical layers are larger in proportion than 

 the other parts; but their uses seem to be 

 the same as in forest trees. 



In bulbous roots, the alburnous sub- 

 stance forms the largest part of the vege- 

 table; but in all cases it seems to contain 

 sap, or solid materials deposited from the 

 sap. The slender and comparatively dry 

 leaves of the pine and the cedar perform 

 the same functions as the large and juicy 

 leaves of the fig tree, or the walnut. 



Even in the cryptogamia, where no 

 flowers are distinct, still there is every 

 reason to believe that the production of 

 seed is effected in the same way as in the 

 more perfect plants. The mosses, and 

 lichens, which belong to this family, have 

 no distinct leaves, or roots, but they are 

 furnished with filaments which perform 

 the same functions; and even in the fungus 

 and the mushroom there is a system for 

 the absorption and aeration of the sap. 



It was stated in the last lecture, that all 

 the different parts of plants are capable of 

 being decomposed into a few elements. 

 Their uses as food, or for the purposes 

 of the arts, depend upon compound ar- 

 rangements of those elements which are 

 capable of being produced either from 

 their organized parts, or from the juices 

 they contain; and the examination of the 

 nature of these substances, is an essential 

 part of agricultural chemistry. 



Oils are expressed from the fruits of 

 many plants, resinous fluids exude from 

 the wood; sacharine matters are afforded 

 by the sap ; and dying materials are 

 furnished by the leaves, or petals of 

 flowers ; but particular processes are ne- 

 cessary to separate the different compound 

 vegetable substances from each other, such 

 as maceration, infusion, or digestion in 

 water, or spirits of wine; but the applica- 

 tion and the nature of these processes will 

 be better understood, when the chemical 

 nature of the substances is known ; the 

 consideration of them will, therefore, be 

 reserved for another place in this lecture. 



The compound substances found in ve- 

 getables are, 1, gum or mucilage, and its 

 different modifications; 2, starch; 3, sugar; 

 4, albumen ; 5, gluten; 6, gum elastic; 

 7, extract; 8, tannin ; 9, indigo; 10, nar- 

 cotic principle; 11, bitter principle; 12, 

 wax; 13, resins; 14, camphor; 15, fixed 

 oils; 16, volatile oils; 17, woody-fibre; 

 IS, acids ; 19, alkalies ; earths, metallic 

 oxides and saline compounds. 



